10 CUCKOOS AND SHKIKES IN RELATION TO AGRICULTURE. 
still remains to be determined. As to the kinds of caterpillars eaten, 
it may be said that the hairy and spiny species far outnumber the 
smooth, bat this may be dne either to the greater abundance of the 
hairy ones or t<> the bird's preference. 
This diet <>f hairy caterpillars has a curious effect upon the birds' 
stomachs. A cuckoo's stomach, unlike that of seed-eating species, has 
only a thin muscular coat on the outside, and the usual smooth lining- 
is almost entirely devoid of ruga* or folds so characteristic of the 
stomachs of many birds. This inner layer is almost always found 
pierced by ai least a few caterpillar hairs; often by so many as to be 
completely furred and the membrane itself almost entirely concealed. 
Incidentally this hairy lining affords an excellent means of determining 
the motion of the food during digestion. If a stomach is divided in the 
plane of its two greater diameters the hairs on each half will be found 
brushed around a center like the nap on the top of a silk hat, indicating 
that the whole mass of food revolves in this plane. It may also be 
noticed that the skins of caterpillars taken from the stomachs of birds 
are always twisted like a cord or rope, and often require considerable 
untwisting before their characters can be determined. 
In a review of the food of cuckoos the most striking point is the 
great number of caterpillars or lepidopterous larvae which enter into 
the year's diet. These insects are crude feeders, eating immense quan- 
tities of vegetable tissue, and are usually so distended with it that the 
amount of real nutrition in any one of them must be small. In fact, 
stomachs of birds that have eaten largely of caterpillars always show 
a quantity of this finely cut vegetable matter derived from the insects' 
stomachs. As digestion in birds is rapid it would seem necessary to 
fill the stomach several times a day with such quickly digested and 
slightly nutritious food as this, while the number of caterpillars found 
in a stomach at any one time probably represents but a small portion 
of the actual daily consumption. From these considerations it appears 
that cuckoos must eat an enormous number of larva' in the course of a 
season. If the contents of all the stomachs examined are regarded as 
so many daily meals of the same bird, then the result indicates that 
the bird has eaten 2,771 caterpillars in 165 consecutive days, at the 
rate of only one meal each day, and some days not eating any. Now, 
166 days is about the length of time that cuckoos remain in their 
Bummer range: moreover, as indicated above, one cuckoo must eat sev- 
eral meals a day, so this number (2.771) probably falls far short of 
the actual number of caterpillars devoured by each cuckoo during the 
Mil. 
In View of such considerations it seems hardly possible to overesti- 
mate the value of the cuckoo's work. All caterpillars are harmful, 
many of them are pests, and any of them are likely to become so. The 
common tent caterpillar formerly fed upon the wild cherry, but has 
now turned it> attention principally to apple trees, sometimes com- 
